Mohamed Morsi was reportedly being held on charges he killed a soldier and conspired with the Palestinian militant group Hamas, as the Egyptian city of Alexandria saw seven killed and over 100 injured in clashes Friday.

The former president, who has not been seen nor heard from since he was ousted by Egypt's military on July 3, has been ordered detained for at least another 15 days, according to Egyptian state media.

A report by the state news agency said investigating judge Hassan Samir had confronted Morsi with evidence during his questioning, though it did not say when or where he had been questioned.

Morsi was one of several members of the Muslim Brotherhood who escaped from the Wadi el-Natroun prison during the 18-day revolt. The charges filed Friday allege that he plotted with Hamas to mount the jail break.

Speaking to Agence France-Presse, Muslim Brotherhood spokesman Gehad el-Haddad dismissed the accusation as "ridiculous" and compared it to "a retaliation from the old regime."

"Hamas condemns this move since it is based on the premise that the Hamas movement is hostile," spokesman Sami Abu Zuhri told AFP. "This is a dangerous development, which confirms that the current powers in Egypt are giving up on national causes and even using these issues to deal with other parties — first among them the Palestinian cause."

The revelation of charges came as pro- and anti-Morsi supporters held rival street protests, raising the specter of more violence in the capital and beyond.

Army General Abdel Fatah al-Sisi had called for mass demonstrations Friday to oppose "terrorism" and provide the military with a "mandate" to maintain order and prevent violence.